The present invention relates to an optical module for multi-channel wavelength division multiplexing. The optical module includes parallel, optical conversion fiber portions, wherein a respective optical conversion fiber portion is associated with a specific dispersion map. Each optical conversion fiber portion transmits a different set of channels of a multi-channel wavelength division multiplexing grid, wherein the channels are regularly spaced from each other.
The invention is based on priority application EP 01 440 131.9, which is hereby incorporated by reference.
The proliferation of a wide range of new services involves rapid growth in the transmission capacity of telecommunications networks. A key issue is the control of the quality of the transmission data along the whole link. Dispersion management (DM) appears to be a very powerful technique for enhancing the quality of wavelength division multiplexing (WDM) transmission systems. The data are transmitted through so-called dispersion-managed pulses or solitons. At higher bit rates (i.e., starting at 40 Gbit/s and above), in-line optical regeneration based on both intensity and phase modulation (IM-PM) is a helpful and powerful tool for enabling error-free transmission over transoceanic distances. Owing to amplitude fluctuations induced by IM, a narrow bandpass optical filter must be added to the synchronous modulation. However, filters have been shown to be of only poor efficiency in stabilizing the energy of a DM soliton.
To overcome this problem, B. Dany et al. proposed in xe2x80x9cTransoceanic 4xc3x9740 Gbit/s system combining dispersion-managed soliton transmission and new xe2x80x9cblack-boxxe2x80x9d in-line optical regenerationxe2x80x9d, Electron. Lett., 1999, 35, (5), pp.418-420, a local periodic conversion between a DM soliton and a standard nonlinear Schrxc3x6ndinger (NLS) soliton, thus restoring the filter efficiency for stabilizing amplitude fluctuations. This procedure was tested for data transmission via a single channel.
In xe2x80x9cSimultaneously regenerated 4xc3x9740 Gbit/s dense WDM transmission over 10,000 km using a single 40 GHz InP Mach-Zehnder modulatorxe2x80x9d, Electron. Lett., 2000, 36, (18), pp.1574-1575, by O. Leclerc et al., a generalization of the above-mentioned procedure for four channels is discussed. A simultaneous optical regeneration (in-line) of the four channels is obtained in a reliable, polarization-insensitive and wavelength-independent Mach-Zehnder packaged modulator. Prior to being optically regenerated, the channels are spectrally demultiplexed. The optical regeneration scheme includes an amplification stage that provides a near NLS soliton average power in a conversion fiber. Hence, at the output of the fiber, DM solitons from each WDM channel are converted into NLS solitons and then spectrally filtered through optical filters having optimized bandwidths. All four WDM channels are then recombined through a multiplexer and simultaneously input in the packaged Mach-Zehnder modulator. Through this approach, all channels are demultiplexed and one fiber per channel is used. Consequently, one dedicated amplifier per channel is needed.
Problems arise when this procedure is applied to dense WDM technology, which is nowadays based on even more than 32 channels. Indeed, one conversion fiber must be provided for each existing channel. And since a dedicated amplifier per channel is needed, this solution is costly. Also, an optimization of the volume when packaging the whole system will be almost impossible.
It is an object of the present invention to reduce the number of conversion fibers and optical amplifiers so as to utilize the above-mentioned procedure when dense WDM technology is involved.
This and other objects are attained by an optical module for multi-channel wavelength division multiplexing. The optical module includes parallel, optical conversion fiber portions, wherein a respective optical conversion fiber portion is associated with a specific dispersion map. Each optical conversion fiber portion transmits a different set of channels of a multi-channel wavelength division multiplexing grid, wherein the channels are regularly spaced from each other.
The present invention is based on the advantageous use of optical conversion fibers not only for a single channel but for sets of channels that are selected, in a precise way, from the used multi-channel WDM grid. The sets of channels are defined such that four wave mixing is negligible or has a negligible effect.
Further advantageous features of the invention are defined in the dependent claims and will become apparent from the following description and the drawings.